PLATE XXXIII. 

 DEEP VIEW OF THE CALF, LONG FLEXORS, &c. 



In thin plate the muscles of the calf hare been removed, the tendo Achillis having 

 been divided just above its insertion into the os calcis, the plantaris and gastrocnemiua 

 entirely removed, while the soleus has been cut away from its fibular origin, leaving the 

 origin from the oblique line and the inner border of the tibia. Lastly, the deep tibial 

 fascia has been removed in order to expose the long flexor muscles and posterior tibial 

 vessels and nerve which lie under it. It is important to bear in mind this dri-p tibial 

 fascia when ligaturing the posterior tibial artery, for unless this be incised much tinn- 

 will be lost in searching for the artery in the space between the fascia and soleus muscle. 

 The fascia stretches across from the tibia to the fibula, being thin above, where it joins 

 the arch of the soleus over the vessels, and gradually thickens as it descends, joining 

 the internal and external annular ligaments respectively. It will bo noticed, on reference 

 to the plate, that very little of the tibialis posticus is seen, it being to a great extent 

 under cover of an aponeurosis, which gives the flexor longus digitorum an origin from 

 the fibula on its postero-internal border ; from the lower part of the aponeurosis some 

 of the fibres of the flexor longus hallucis arise. This aponeurosis has been named the 

 deep intermuscular septum, and in well-marked muscular subjects is occasionally 

 replaced by muscle fibres which belong chiefly to the origin of the flexor longus 

 digitorum. 



The long flexor muscles are repeated in most mammalian orders, forming there as 

 in man the deep layer, the flexor longus hallucis having as its homologue the flexor 

 fibularis, and the flexor longus digitorum the flexor tibialis, the tibialis posticus 

 remaining the same. But while the flexor fibularis exists in all species with but little 

 variation, the flexor tibialis and tibialis posticus may vary greatly in size, and in some 

 varieties of marsupials (Macropodidffl) both the latter muscles are either rudimentary or 

 wanting, the flexor fibularis alone remaining. In some of the bats the conditions are 

 reversed, the flexor tibialis being the larger and displacing the flexor fibularis.' 



In order to render the deep view complete a separate sketch has been added showing 

 the popliteus muscle, and also the lower posterior nerve supply of the joint ; the origin 

 of the popliteus from the posterior ligament of the knee, as well as its tendinous origin 

 from the femur, is well shown. This deep view also shows how closely the fibres of 

 the peroneus longus are connected at their origin with the external lateral ligament ot 

 the knee-joint, in fact some of the fibres often arise from its base. In the opossum, 

 ox, and gibbon the peroneus longus arises directly from the external condyle of the 

 femur and replaces the ligament, the tendon having no attachment to the fibula, and 

 thus permitting free rotation. In the human foetus as late as the fourth month the 

 ligament and peroneus longus are in direct continuity, the muscle having but a slight 

 attachment to the fibula. Thus the external lateral ligament is probably the lost tendon 

 of the peroneus longus. 2 



1 Dobson, Journal Anat. and Phyi. vol. XYU. p. 142. 

 1 Bland Button, Ligamentt Natvn and Morphology. 



